There is known a projection-type display apparatus that projects a personal computer picture, a video image or the like to a screen. The projection-type display apparatus includes a light source device, and a display device such as a DMD (Digital Micromirror Device) or a LCD (Liquid Crystal Display) panel that modulates light. Light from the light source device is modulated by the display device, and a desired image is displayed on the screen.
The brightness of the image that is projected from the projection-type display apparatus is determined based on the brightness of the light that is emitted from the light source device disposed in the projection-type display apparatus. Accordingly, in the projection-type display apparatus, the light source device that includes a high-pressure mercury lamp capable of emitting relatively bright light has been used.
However, because the high-pressure mercury lamp contains mercury, there is a possibility that the mercury will leak and contaminate the environment when the high-pressure mercury lamp is discarded. Thus, JP2009-277516A (hereinafter, Patent Literature 1) discloses, as a light source device that does not contain any such environmental pollutants as mercury, a light source device that uses a phosphor.
The light source device that is disclosed in Patent Literature 1 includes the phosphor that is excited to emit light, and an excitation light source that emits the excitation light of a blue band to excite the phosphor. The excitation light that is emitted from the excitation light source is applied to the phosphor to excite the phosphor, and the phosphor emits light other than blue band light, such as red band light or green band light. The light source device causes the light (hereinafter, fluorescent light), which is emitted from the phosphor, to enter the display device, and the projection-type display apparatus displays an image on the screen.
The brightness of the image that is projected from the projection-type display apparatus depends on the brightness of the light that is emitted from the light source device. The brightness of the light that is emitted from the light source device that is disclosed in Patent Literature 1, namely, the brightness of the fluorescent light, depends on the amount of excitation light applied to the phosphor. Accordingly, JP2011-13313A (hereinafter, Patent Literature 2) discloses a light source device that includes a plurality of arrayed excitation light sources.
The light source device that is disclosed in Patent Literature 2 will be described referring to FIG. 1.
FIG. 1 is a schematic plan view showing the light source device that is disclosed in Patent Literature 2. As shown in FIG. 1, light source device 1 includes fluorescent wheel 2 where a phosphor layer has been formed, and a plurality of light sources 3 that emit excitation light to excite the phosphor.
The plurality of light sources 3 emits the excitation light in first direction X. Light source 3 includes collimator lens 4 for converting the excitation light, which is emitted from light source 3, into parallel light. Thus, a group of excitation lights that are emitted from light source 3 enters virtual surface A perpendicularly intersecting first direction X, and travels without spreading.
Fluorescent wheel 2 is disposed in the direction along which the excitation light that is emitted from light source 3 travels, and condenser lens group 5 is disposed between light source 3 and fluorescent wheel 2. The group of excitation lights that are emitted from light source 3 is condensed by condenser lens group 5 to be applied to the phosphor layer of fluorescent wheel 2.
The excitation light is applied to the phosphor layer of fluorescent wheel 2, and the phosphor emits fluorescent light. The fluorescent light is dispersed toward light source 3 to pass through condenser lens group 5, and is converted into parallel light within virtual surface A by condenser lens group 5, and then travels toward light source 3.
Between condenser lens group 5 and light source 3, dichroic mirror 6 that reflects the fluorescent light and that lets the excitation light pass is disposed. Accordingly, the fluorescent light that passed through condenser lens group 5 is reflected at dichroic mirror 6 and travels in reflection direction R that intersects first direction X. The fluorescent light that is reflected at dichroic mirror 6 enters virtual surface B perpendicularly intersecting reflection direction R, and then exits from light source device 1 to the outside.
It is known that lights condensable on the display device among lights that are emitted from the light source device are correlated based on Etendue that is one of characteristics of an optical system. When the Etendue of a light source side optical system including the light source device and the Etendue of a projection side optical system including the display device do not satisfy predetermined conditions, the brightness of the light that is emitted from the light source device is not sufficiently condensed on the display device. In other words, lights that are not used for modulation of the display device from among the lights that are emitted from the light source device increase, and the brightness of the image that is projected by the projection-type display apparatus becomes lower.
Conditions between the Etendue of the light source side optical system and the Etendue of the projection side optical system, that uses more of the light that is emitted from the light source device, will be described.
According to JP2005-345767A (Patent Literature 3), the Etendue of the light source side optical system including a surface light source such as a LED light source is expressed by the following formula.Elight=πAlight sin2 θlight  [Formula 1]                Elight: Etendue of light source side optical system        Alight=exit area of light source device        θlight=maximum light-emitting angle of light source device        
According to JP2007-507755A (Patent Literature 4), the Etendue of the projection side optical system including the display device is expressed by the following formula.
                              E          DM                =                              π            ⁢                                                  ⁢            A                                4            ⁢                                          (                                  f                  /                  #                                )                            2                                                          [                  Formula          ⁢                                          ⁢          2                ]                            EDM=Etendue of projection side optical system        ADM=area of display device        f/#: one measure (also referred to as F-number) of the relative aperture of the projection lens        
For example, when the DMD is used as a display device, if the following formula is satisfied, the display device can use the relatively great amount of light that is emitted from the light source device.Elight≦EMD  [Formula 3]
When the LCD panel is used as a display device, if the following formula is satisfied, the display device can use the relatively great amount of light that is emitted from the light source device.2Elight≦EMD  [Formula 4]
As can be understood from formulas 1 to 4, to use the light that is emitted from the light source device more efficiency, preferably, the exit area of the light source device should be smaller while the area of the display device should be bigger.
When the area of the display device is bigger, the outer size of the display device increases, thus the projection-type display apparatus become bigger. The display device is relatively high in price compared to the other components of the projection-type display apparatus. Accordingly, when the display device becomes bigger, the display device becomes higher in price, thereby leading to an increase in the manufacturing costs of the projection-type display apparatus. Thus, there is a request for reducing the size of the exit area of the light source device.
The exit area of light source device 1 that is disclosed in Patent Literature 2 corresponds to the area of virtual surface B, as shown in FIG. 1. The area of virtual surface B depends on the area of virtual surface A. In other words, when the number of light sources 3 increases, the area of virtual surface A is enlarged, thereby causing the size of the exit area of light source device 1 to increase. Thus, in light source device 1 that is disclosed in Patent Literature 2, the number of light sources 3 cannot be increased because of the restrictions of the exit area. The result is limited improvement in the brightness of light source device 1.
Particularly, light source 3 that emits the excitation light frequently generates heat. Consequently, when light sources 3 are arranged close to each other, the heat of light source 3 cannot be efficiently discharged, and the life of light source 3 is easily shortened. In light source device 1 that is disclosed in Patent Literature 2, there has been a greater limit on the number of light sources 3 that emits the excitation lights due to the need to form a sufficient gap between light sources 3. Thus, the inventors have invented a light source unit that emits one group of excitation lights that are formed by collecting excitation lights, which are emitted from arrayed light sources 3, within a narrower range
The light source unit that is invented by the inventors will be described referring to FIGS. 2 and 3.
FIG. 2 is a perspective view showing the light source unit that is invented by the inventors. FIG. 3 is a schematic plan view showing a light source device that uses the light source unit shown in FIG. 2. Components similar to those shown in FIG. 1 will be denoted by similar reference numerals, and description thereof will be omitted.
As shown in FIGS. 2 and 3, light source unit 7 includes a plurality of light sources 3 that emit excitation light in first direction X1, and a plurality of reflection mirrors 8 disposed on the path along which the excitation light, which is emitted from light source 3, travels. Reflection mirror 8 reflects the excitation light in second direction X2 that intersects first direction X1.
Gap D1 in first direction X1 between adjacent reflection mirrors 8 is smaller than gap D2 in second direction X2 between adjacent reflection mirrors 8. Accordingly, the area of virtual surface C that perpendicularly intersects second direction X2, where an excitation light group traveling in second direction X2 enters, is smaller than that of virtual surface D where an excitation light group traveling in first direction X1 enters.
As an example, a group of excitation lights will be discussed, wherein the excitation lights are emitted from twenty four light sources 3 arrayed by 3 in a longitudinal direction (paper surface depth direction in FIG. 3) and 8 in a horizontal direction (paper surface left-and-right direction in FIG. 3), and light source 3 emits parallel light of φ5 mm. When a gap between adjacent light sources 3 is 12 mm, virtual surface D is formed into a rectangular shape where a horizontal size is about 90 mm and the longitudinal size is about 30 mm. When gap D1 in first direction X1 between adjacent reflection mirrors 8 is 5 mm, virtual surface C is formed into a rectangular shape where the horizontal (paper surface up-and-down direction in FIG. 3) size is about 40 mm and the longitudinal (paper surface depth direction in FIG. 3) size is about 30 mm
Thus, light source unit 7 shown in FIGS. 2 and 3 collects the excitation lights, which are emitted from arrayed light sources 3, within the narrower range and emits them in second direction X2. Accordingly, in light source device 9 that uses light source unit 7, the number of light sources 3 can be increased without enlarging the exit area of light source device 9 as compared with light source device 1 shown in FIG. 1. As a result, the brightness of light source device 9 is improved while the exit area is maintained, and an image that is projected by the projection-type display apparatus is brighter without enlarging the display device or increasing costs.
However, reflection mirror 8 shown in FIGS. 2 and 3 can only collect the plurality of excitation lights, which are emitted into and which are output from virtual surface D directed in one direction, within virtual space C. In other words, reflection mirror 8 cannot emit the excitation lights, which enter from the plurality of different directions, in one direction, and thus the number of light sources cannot be further increased without enlarging the exit area.